Compensated amplifier



Dec. 18, 1934. j G ACEVES 1,984,450

COMPENSATFID AMPLIFIER Filed Feb. 3, 1931 2 Sheets-Sheet l INVENTOR 'BYZV; ATTORNEY J. G. ACEVES 1,984,450

COMPENSATED AMPLIFIER Filed Feb. 3, 1931 2 Sheets-Sheet 2 -1 I I I M I I I I I I II INVENTOR BY 7 ATTORNEY Patented Dec. 18, 1934 COMPENSATED AMPER Julius G. Aceves, New York, N. Y., assignor, by mesne assignments, to Louis Gerard Pacent, New York, N. Y.

Application February 3, 1931, Serial No. 513,061. 9 Claims. (Cl. 179-471) This invention relatesto compensated amplifluse ahead oi an amplifier and adapted more ers and has for an object to selectively control especially for use with an electric phonograph the gain of an amplifier for different frequencies. pick-up. In this figure, the input terminals are The invention is of particular utility for conshown at the left and it will be understood that trolling tone in recording and reproducing sounds these are suitably connected with the circuit 5 and other objects of the invention are to reinwhich is to be controlled, such for instance, as force certain desirable frequencies which, under the circuit of an electric phonograph pick-up. ordinary circumstances, are more or less lost and One side of the input, that is the upper side 1 in to subdue other undesirable frequencies. Acthe illustration is branched and one of these cording to the invention, provision is made for branches, the one designated 2 in the diagram is 10 transmitting the low frequencies and the high designed to accentuate the lower frequencies, frequencies with greater voltage amplification while the other, that is the branch 3 is designed than the intermediate frequencies, thereby makto accentuate the high frequencies. These have ing it possible to selectively amplify the difbeen descriptively called a bass booster and a ferent registers faithfully to produce vocal or treble booster. The first includes a condenser 15 instrumental sounds. In particular, the inven- 4 and inductance 5 connected in series across the tion aims to effect reinforcement of the bass line and with the inductance shunted byavariable tones in the range below 100 cycles per second resistance 6. The so-ualled treble booster is and to reinforce the treble tones above the 1,000 shown as made up of a condenser '7 in series with cycles per second. Also, in connection with a resistance 3 across the line, which resistance 20 phonograph pick-up devices, the invention aims has a variable shunt circuit 9 including the prito eliminate the so-called scratch or surface noise mary 10 of a transformer 11. The secondary 12 and to reduce or eliminate the effect of cabinet of the transformer 11 is also directly connected or loud speaker resonance. through the battery 13 with the grid of the ampli- The invention may be embodied in a compenfying tube 14 and has its other terminal so con- 25 sator to be used ahead of an amplifier or may be nected to the bass booster that with respect to the embodied in an amplifier as an integral part input circuit of the tube 14, the E. M. F. developed thereof. With either embodiment, selective com in the secondary acts in series relation with the trol of the low, intermediate and high registers E. M. F. developed by the bass booster.

is provided by means of which the amplifica- The values of the bass reinforcing branch are 30 tion of the various registers may be differentially selected to transmit high and intermediate freeliected. quencies without increase in the degree of voltage The invention has utility wherever it is desired amplification and to transmit low frequencies with selectively to amplify different frequencies, but increase in the degree of voltage amplification for the sake of simplicity, the invention is spewhile the values in the treble reinforcing branch 35 cifically disclosed in connection with audio freare selected to transmit substantially all high frequency amplifiers. The drawings accompanying quencies with increase in the degree of voltage and forming part of the invention illustrate diamplification. The outputs of these selecting agrammatically practical embodiments of the branches, by being connected in series relation invention, but it should be understood that the feed directly into the amplifying tube, so that 40 actual structure may be modified within the inwith this simple arrangement, the desirable lower tended broad scope of the invention. frequencies are brought out and at the same time Other objects, novel features and advantages the treble or higher frequencies are saved. The of this invention will be apparent from the folextent of reinforcement or amplification of these lowing specification and accompanying drawings, I particular frequencies may be regulated by ad- 45 wherein: justment of the variable resistance 6 in the bass Fig. 1 is a diagrammatic illustration of one reinforcement branch and the variable resistance embodiment of the invention. 8 in the treble reinforcement branch.

Fig. 2 is a diagrammatic illustration of a second,v Thus the amount of gain or reinforcement of embodiment of the invention. both the bass and upperregister may be ade- 50 Fig. 3 is a diagrammatic illustration of a third quately controlled. As a further measure, the

embodiment of the invention, and leakage inductance and the distributed capacity Fig. 4 is a diagrammatic illustration of a fourth of the secondary in the transformer 11 may, by embodiment of the invention. suitable transformer design be made to reinforce Fig. 1 illustrates an embodiment intended for the upper register. 55

The means for reducing objectionable speaker resonance and for suppressing the surface noise are directly associated in the present disclosure with the output of the amplifying tube and such means comprise, in the present instance, sharply tuned resonant circuits.

In the illustration, 2, parallel feed path is connected across the output of the tube, including an inductance 15 in series with the plate potential source 16. The so-called speaker resonance suppressor is shown as consisting of a variable resistance 17, the variable inductance 18 and condenser 19, in series relation across the output circuit and the surface noise suppressor is shown as a variable inductance 20 and condenser 21 in series across the line parallel with the resonance suppressor.

As the majority of record scratch is found to be located in the vicinity of 3800 cycles, the eliminator circuit 20, 21, is tuned to this frequency and therefore shunts out the record scratch or surface noise. The speaker resonance circuit is tuned quite sharply to the resonance frequency of the speaker and its associated chain and when the two circuits last described are properly adjusted, they may require no further attention from the operator.

Additional means for reinforcing certain of the bass frequencies may be provided, if desired, the same being shown in the illustration as a circuit of the parallel resonance type, consisting of an inductance 22 and condenser 23 in parallel across the line with a variable resistance 24 in series, for quantitative adjustment. Once properly set, this circuit may not require further adjustment by the operator.

The output from the control system described may be passed directly into the first stage of an amplifier, under control of a fader 25.

The arrangement and combination disclosed enable the resonance of the natural periods of different speakers and auditoriums to be corrected for as needed. Alsowith this combination, the desired reinforcement or attenuation of selected frequencies may be determined at will. The structure is relatively simple and may be efficiently combined with existing forms of apparatus. Fig. 2 illustrates an embodiment generally similar to the embodiment illustrated in Fig. 1, but adapted more especially for connecting a loud speaker to an audiofrequency supply line for the purpose of modifying the relative intensities at various frequencies and thereby improve the quality.

The input circuit is bridged by a. potentiometer 26, by means of which volume control is effected. The upper side 1 of the input circuit is branched and the branch 2 is designed to accentuate the lower frequencies while the branch 3 is designed to accentuate the high frequencies. Across the line the bass booster" includes a condenser 4 and inductance 5 connected in series and a variable resistance 6 is shunted around the inductance 5. The treble booster is made up of a condenser '7 in series with a resistance 8 across the'line, the resistance having a variable shunt 9 including the primary 10 of a transformer 11 whose secondary 12 is connected in series relation with the other booster at one side and at the other side to the grid of the amplifying tube 14. As previously described. the amount of gain of both the low and upper register may be controlled.

A parallel feed path is connected across the output of the tube and includes an inductance 15 in series with the plate potential source 16. A shunt circuit consisting of variable inductance 18a and condenser 19a is of proper value to transmit cabinet or loud speaker or room resonant frequencies with voltage attenuation thereby subduing such frequencies. A shunt circuit consistlngof the variable resistance 20a and the condenser 21a is of proper value to transmit high frequencies with voltage attenuation and thus subdue the frequencies impressed across the double impedance 25a, the extent to which such frequencies are attenuated being regulated by the value of the resistance 20a. The coupling condenser 27 in conjunction with the impedance 25a is of proper value to transmit low frequencies with voltage amplification and the resistance 28 regulates the boosting effect of the same. The arrangement illustrated in Fig. 2 permits reinforcement or attenuation of selected frequencies at will in the same manner as the embodiment disclosed in Fig. 1.

Fig. 3 illustrates an embodiment intended for use ahead of an amplifier. A wave source 30 such as a microphone or phonograph pick-up has one terminal connected to a resistance 31 which is in turn connected to a potentiometer 32. The resistance 31 is shunted by condenser 33 connected in series with a variable resistance 34. The potentiometer 32 is connected to the primary of a step-up transformer 35 through a condenser 36 and a variable resistance 37 is connected in shunt to the primary of the transformer. secondary of the transformer 35 is connected to the input circuit of an electron discharge device 38.

The network consisting of the resistances 31 and 34 and the condenser 33 is so designed as to be effective to attenuate the low and intermediate frequencies relative to the high frequencies, the extent of attenuation of the low and intermediate frequencies being regulated by varying the resistance 34. The network consisting of the condenser 36, inductance 35 and resistance 37 is designed to be effective to accentuate low frequencies over the high and intermediate frequencies, the extent of accentuation being regulated by varying the resistance 37. The potentiometer 32 controls the volume.

With the circuit above described, selective control of the low, intermediate and high registers is provided. The low and intermediate frequencies are bothsubdued by the circuit 31, 33"

and 34 and then the low frequencies are accentuated without corresponding accentuation of the intermediate frequencies. By proper control of the extent of attenuation of the low and intermediate frequencies and the subsequent accentuation of the low frequencies, the required relationship of the three registers for faithful reproduction of vocal or instrumental sounds is obtained.

Fig. 4 discloses an amplifier having the compensator as an integral part thereof. A detector tube 40 has its grid and cathode connected through a tuned circuit 41 with an antenna 41a. In the space current circuit for the detector tube 40 a resistance 42 is arranged in series with an inductance 43 around which is shunted a variable resistance 44. The input circuit of an amplifier tube 45 is coupled to the output circuit of the detector tube 40 through a condenser 46 and is bridged by an inductance 4'7 shunted by a variable resistance 48. In the space current circuit of the amplifier tube 45 is provided a resistance 42a in series with an inductance 43a shunted by a variable resistance 44a. The input circuit of a second amplifier tube 49 is coupled to the The (ill

output circuit of the first amplifier tube through a condenser 46a and is bridged by an inductance 47a shunted by a variable resistance 48a. The output circuit of the amplifier 49 is inductively connected through the transformer 50 with a push-pull circuit 51 which operates in the well-known manner.

The network comprising the resistances 42 and 44 and the inductance 43 is designed to transmit a selected high frequency with increase in its degree of voltage amplification while the network containing the inductance 4'7 and resistance 48 is designed to transmit a selected low frequency with increase in its degree of voltage amplification, thereby accentuating these frequencies, the extent of accentuation being regulated by the resistances 44 and 48.

The network containing the resistances 42a and 44a and the inductance 43a is designed to accentuate a slightly different high frequency than that accentuated by the corresponding prior network and the network containing the inductance 47a and resistance 48a is designed to accentuate a slightly different low frequencythan that accentuated'by the corresponding prior network, the extent to which these networks. accen-- tuate the selected frequencies being regulated by the resistances 44a and 4811. By having the corresponding networks accentuate slightly different frequencies, sharp amplification peaks are avoided and a broader range of control is provided. The low and high frequencies are controlled in their amplification independently of each other and also independently of the amplification of the intermediate frequencies so that effective selective compensation is obtainable to reproduce faithfully instrumental and vocal sounds. With this compensator, both the low and high fre quencies are accentuated over the intermediate frequencies.

It is to be understood that the embodiments of the'invention above described are merely illustrative of the invention and that various changes and modifications may be made in these embodiments, without in any way departing from the spirit of the invention as defined in the appended claims.

This application is a continuation in part of the co-pending application of Julius G. Aceves, Serial No. 459,246, filed June 4, 1930.

I claim:

1. Apparatus of the character described comprising a vacuum tube circuit, a second vacuum tube circuit having its input capacitatively connected to the output of the first circuit, means in the output of the first circuit for accentuating a selected band of high audio frequencies, and

means in the input of the second circuit for accentuating a selected band of low audio frequencies.

2. Apparatus of the character described comprising a vacuum tube circuit, a second vacuum tube circuit having its input capacitatively connected to the output of said first circuit, an inductance shunted by a variable resistance in the lected band of high audio frequencies and an inductance shunted by variable resistance bridged across the input of the second circuit for accentuating a band of selected low audio frequencies.

3. Apparatus of the character described comprising a vacuum tube circuit, a second vacuum tube circuit having its input capacitatively connected to the output of the first vacuum tube circuit, a third vacuum tube circuit having its input capacitatively connected to the output of the second vacuum tube circuit, means in the outputs of the first and second circuits for accentuating different selected bands of high audio frequencies, and means in the inputs of the second and third circuits for accentuating different selected bands of low audio frequencies.

4. In a device of the character described, a vacuum tube amplifier, and an input circuit therefor comprising means for attenuating selected low and intermediate audio frequency bands, and means for subsequently accentuating the low audio frequency band.

5. In a device of the character described, a vacuum tube amplifier, and an input circuit therefor comprising means for separating low audio frequencies from the high and intermediate audio frequencies, means for accentuating selected high audio frequencies, means for accentuating selected low audio frequencies, and means for combining the intermediate and accentuated high frequencies with the accentuated low frequencies.

6. In a device of the character described, a vacuum tube amplifier, and an input circuit therefor comprising means for attentuating low and intermediate audio frequencies and means in series therewith for accentuating selected low audio frequencies.

7. In a device of the character described, a network comprising a resistance shunted by a variable resistance and a condenser, a second net work comprising a condenser in series with an inductance shunted by a resistance, said circuits being connected in concatenation, a vacuum tube having its input circuit inductively connected with said inductance, said first circuit being adapted to attenuate low and intermediate audio frequencies and said second circuit being adapted to accentuate low audio frequencies.

8. In a device of the character described, a vacuum tube circuit, a second vacuum tube circuit having its input capacitatively connected to the output of the first circuit, a network in the output of the first circuit for accentuating a selected band of high audio frequencies, and a network in the input of the second circuit for accentuating a selected band of low frequencies.

9. In a device of the character described, a vacuum tube amplifier, an input circuit therefor comprising means for attenuating selected low and intermediate frequency bands, means for accentuating selected high audio frequencies, and means for subsequently accentuating the attenuated low frequencies.

JULIUS G. ACEVES.

output of thefirst circuit for accentuating a se- 

